The terms "probiotics" is attributed to Parker (20) who defined them as "organisms and substances which contribute to intestinal balance" when used as dietary supplements. This publication and all other publications and patents cited herein are incorporated herein by reference. Later, Fuller (11) considered this definition to be too broad since, in addition to including cell cultures and microbial metabolites, it could encompass antibiotic preparations. More recently, a number of summaries have appeared in the literature describing the scientific basis for use of probiotics as intestinal inoculants for production animals (10, 26). It has been suggested that the term "probiotics" be replaced by the term "direct feed microorganisms," or DFM's (9).
The concept of adding viable, harmless lactic acid bacteria to the gastrointestinal tract as a dietary supplement was first appreciated by Metchnikoff (16) who viewed the consumption of yoghurt by Bulgarian peasants as conferring a long span of life. Some workers have claimed that the therapeutic value derived from ingestion of such fermented milk products is related to the viable bacteria present in these products (12, 27). Since Metchnikoff's early reports, several studies have shown the ability of lactobacilli, for example, to suppress coliform growth. Feeding viable Lactobacillus acidophilus cells to young dairy calves was shown to reduce the incidence of diarrhoea (3), and increase the numbers of lactobacilli and reduce coliform counts in feces (4). These findings contrast with those of others who were unable to demonstrate benefits from feeding either Lactobacillus acidophilus (8, 13) or milk cultured with Lactobacillus acidophilus or Lactobacillus lactis (17).
In a detailed study by Muralidhara et.al. (18), piglets given a Lactobacillus lactis concentrate for up to 8 weeks after birth showed a progressive decline in coliform counts in fecal samples. Scouring in these animals was negligible, but was evident in control pigs especially at weaning. Underdahl et al. (32) observed only mild diarrhoea lasting 2-4 days in gnotobiotic pigs inoculated with Streptococcus faecium prior to artificial Escherichia coli infection. In the same study, persistent diarrhoea occurred in pigs similarly infected with Escherichia coli, but without prophylactic treatment with the Streptococcus microorganism.
Probiotics (hereafter referred to as DFM's) are bacterial or yeast preparations that are administered orally or added to feeds. The most commonly used DFM's are strains of the lactic acid bacteria (LAB), particularly those classified in the following genera: Lactobacillus, Latcococcus, and Enterococcus. Included among these are the following species: Lactobacillus acidophilus, Lactobacillus bulgaricus, Lactobacillus plantarum, Lactobacillus casei, Lactobacillus lactis, Latcococcus lactis, Latcococcus thermophilus, Latcococcus diacetylactis, and Enterococcus faecium. Besides these LAB, some species of Bacillus (Bacillus subtilis, Bacillus toyoi) and yeasts and molds (Saccharomyces cerevisiae, Aspergillus oryzae, and Torulopsis sp.) are used as DFM's (10).
It is generally held that during periods of low resistance, such as stress, undesirable microorganisms are able to proliferate in the GI tract of animals, humans included. Maintaining a normal, healthy balance of microorganisms is deemed to be critical during such stressful periods (10). The concept underlying use of DFM's, therefore is that if sufficient numbers of an appropriate microorganism(s) are introduced into the intestinal tract (i) at times of stress and/or disease, (ii) at birth, or (iii) after antibiotic treatment (when minimal LAB are present), the negative consequences of the microbial imbalances can be minimized or overcome. Using such preparations of live, naturally occurring microorganisms helps restore and maintain the proper balance of beneficial microbes in the GI tract during times of stress, disease, and following antibiotic therapy (10). This concept, descriptions of proposed modes of action, and evidence for the efficacious uses of DFM's for all production animals are summarized in reviews by Fox (10), Sissons (26), and by various authors (22).
One of the major problems or limitations encountered in commercial scale application of DFM's to animals is (i) the availability of suitable delivery systems, and (ii) the ability to get the probiotic preparations to the animals as quickly as possible after birth. This is particularly true when pelletized feeds are used, as is the case in the poultry industry. The pelletization process generally includes one or more heating steps involving temperatures high enough to pasteurize or sterilize the feed components, thereby precluding incorporation of viable microorganisms into these feeds prior to pelletization.
The present invention describes novel methods and processes for overcoming some of these problems, by delivering viable DFM's in feed additives. The DFM used to develop these methods is Lactobacillus reuteri. This species was chosen because it has demonstrated efficacy as a DFM in poultry (21). Previous patent applications have been submitted relating to unique properties of the species. These applications are: PCT/US88/01423, filed Apr. 28, 1988 and published Nov. 3, 1988, claiming priority from U.S. Ser. No. 07/268,361 filed Sep. 19, 1988 which is a continuation-in-part of U.S. Ser. No. 07/102,830 filed Sep. 22, 1987 which is a continuation-in-part of U.S. Ser. No. 07/046,027 filed May 1, 1987; and U.S. Ser. No. 07/539,014 filed Jun. 15, 1990. The disclosure of these applications is incorporated herein by reference.
Lactobacillus reuteri is a species of lactic acid bacteria recognized since the turn of the century (19). Originally assigned different species names (e.g., Lactobacillus fermentum biotype II), it obtained distinct species status in 1980 and is registered in the 1988 edition of Bergey's manual (14, 15). It is found in foods, particularly dairy products and meats, but exists primarily in the GI tract of healthy animals, including humans (1, 6, 7, 14, 15, 23, 24, 25, 33).
Lactobacillus reuteri is the dominant heterofermentative Lactobacillus inhabiting the GI tract (23, 24, 25). It is a typical heterofermenter, converting sugars into acetic acid, ethanol, and CO.sub.2 in addition to lactic acid which is the major endproduct of homofermentative metabolism carried out by species such as Lactobacillus acidophilus (31). It utilizes the phosphoketolase pathway for conversion of glucose to endproducts. When glycerol, an alternate hydrogen acceptor, is present in the culture medium together with glucose or other utilizable carbon and energy sources (e.g., lactose), acetate rather than ethanol accumulates, and the glycerol is reduced to 1,3-propanediol via the metabolic intermediate, 3-hydroxypropionaldehyde (3-HPA). 3-HPA has been shown to have potent antimicrobial activity, and Lactobacillus reuteri appears to be unique among microorganisms examined to date in its ability to secrete this substance, termed reuterin, into the surrounding medium (2, 5, 7, 28, 29, 30, 31). This unique antimicrobial activity may play a role in competitive survival of this species in the gastrointestinal ecosystem, and/or its ability to regulate growth and activities of other microorganisms in this ecosystem (7). It is thus very important to establish this microorganism early in animals. It is therefore an object of the invention to provide a method for delivering DFM's, such as Lactobacillus, to avian species.
Other objects and advantages will be more fully apparent from the following disclosure and appended claims.